When a hard-switching fault occurs, a high short-circuit current flows through a power semiconductor element such as an IGBT and a MOSFET, which may cause thermal destruction of the power semiconductor element. Accordingly, there is a need for functions of detecting a short-circuit state in the power semiconductor element, and protecting the power semiconductor element.
PTD 1 (Japanese Patent Laying-Open No. 2001-197724) discloses a drive circuit for a power semiconductor element. The drive circuit is configured to detect a voltage across main terminals of the power semiconductor element (a collector-emitter voltage in an IGBT) to determine that an overcurrent state or a short-circuit state occurs when the voltage across the main terminals is higher than a prescribed determination value.
PTD 2 (Japanese Patent Laying-Open No. 2007-259533) discloses a protection circuit configured to detect a collector current and a gate-emitter voltage in a power semiconductor element (IGBT). Under the hard-switching fault operating condition, the gate-emitter voltage rises to a gate drive power supply voltage at once, and a high collector current flows therethrough. Accordingly, when the gate-emitter voltage is higher than a prescribed voltage that is set in advance, and when the collector current value is higher than a prescribed current value that is set in advance, it is determined that the hard-switching fault occurs.
On the other hand, PTD 3 (U.S. Pat. No. 3,883,925) discloses a configuration of a drive circuit for detecting a hard-switching fault only based on the gate-emitter voltage of a power semiconductor element (IGBT). Particularly, in the hard-switching fault, the so-called mirror period observed under the normal operating condition does not appear. Accordingly, the hard-switching fault is detected as the gate-emitter voltage exceeds a reference value in the detection time period corresponding to a mirror period.